JP7764801B2 - Coverage calculation method, charged particle beam lithography method, coverage calculation device, and charged particle beam lithography device - Google Patents

Description

The present invention relates to a coverage calculation method, a charged particle beam drawing method, a coverage calculation device, and a charged particle beam drawing device.

As LSIs become more highly integrated, the circuit line widths required for semiconductor devices are becoming finer every year. To form the desired circuit patterns on semiconductor devices, a method is adopted in which a high-precision master pattern formed on quartz is reduced and transferred onto a wafer using a reduction projection exposure system. To produce high-precision master patterns, a technique known as electron beam lithography is used, in which a resist is exposed to light using an electron beam writing system to form the pattern.

One known example of an electron beam lithography device is a multi-beam lithography device that uses multiple beams to irradiate multiple beams at once, improving throughput. In this multi-beam lithography device, for example, an electron beam emitted from an electron gun passes through an aperture member with multiple openings to form multiple beams, and blanking of each beam is controlled by a blanking plate. The unblocked beam is reduced in size by an optical system and irradiated onto the desired position on the mask to be lithographed.

A multi-beam drawing device calculates the pattern coverage (area density) for each pixel (pixel) that divides the drawing area into a mesh, and adjusts the irradiation dose of each beam of the multi-beam according to the coverage. The smaller the pixel size, the more accurately the pattern shape is reflected, improving resolution and drawing accuracy. However, as the pixel size decreases, there are problems such as an increase in the time required to calculate coverage and an increase in memory usage for storing the coverage calculation results.

For example, as shown in Figures 9(a) and 9(b), when the pixel size (the length of one side of a pixel) is reduced from 16 nm to 4 nm, the number of calculations for the coverage increases from 1 to 4. Furthermore, the memory usage for storing the calculation results of the coverage increases from 2 bytes to 32 bytes. By reducing the pixel size by 1/n (n is an integer equal to or greater than 2), the number of calculations increases by n times, and the memory usage increases by ⁿ² times.

Japanese Patent Application Laid-Open No. 2005-340438 JP 2012-230689 A WO 2008/084543

The present invention aims to provide a coverage calculation method, a charged particle beam drawing method, a coverage calculation device, and a charged particle beam drawing device that can reduce the amount of pixel coverage calculation and memory usage.

A coverage calculation method according to one aspect of the present invention is a method for calculating the pattern coverage for each pixel region obtained by dividing a drawing region in which a pattern is drawn by irradiating a charged particle beam with a predetermined size. The method virtually divides the drawing region by a first size to generate a plurality of first pixel regions, calculates the pattern coverage for the first pixel regions, virtually divides the first pixel region by a second size smaller than the first size to generate a plurality of second pixel regions corresponding to the pixel regions, selects a second pixel region that approximates the pattern shape within the first pixel region, and calculates the pattern coverage for the selected second pixel region based on the pattern coverage for the first pixel region, the number of second pixel regions within the first pixel region, and the number of selected second pixel regions.

A charged particle beam writing method according to one aspect of the present invention calculates the irradiation dose for each pixel region using the coverage of the second pixel region calculated by the above-described coverage calculation method, and controls the charged particle beam based on the calculated irradiation dose to write a pattern on a substrate.

A coverage calculation device according to one aspect of the present invention is a coverage calculation device that irradiates a charged particle beam and calculates the pattern coverage for each pixel region obtained by dividing a drawing region in which a pattern is drawn by a predetermined size. The coverage calculation device virtually divides the drawing region by a first size to generate a plurality of first pixel regions, calculates the pattern coverage for the first pixel regions, virtually divides the first pixel region by a second size smaller than the first size to generate a plurality of second pixel regions corresponding to the pixel regions, and has a rasterization unit that selects the second pixels that approximate the pattern shape within the first pixel region. The coverage calculation device calculates the pattern coverage for the selected second pixel regions based on the pattern coverage for the first pixel region, the number of second pixel regions within the first pixel region, and the number of selected second pixel regions.

A charged particle beam lithography apparatus according to one aspect of the present invention includes a dose map creation unit that calculates the irradiation dose for each pixel region using the coverage of the second pixel region calculated by the coverage calculation device and creates a dose map that defines the irradiation dose for each pixel region; an irradiation time calculation unit that calculates the irradiation time for each pixel region based on the dose map; and a lithography control unit that controls the irradiation dose of the charged particle beam based on the calculated irradiation time.

This invention reduces the amount of pixel coverage calculation and memory usage.

1 is a schematic diagram of a multi-charged particle beam writing apparatus according to an embodiment of the present invention; 10A and 10B are diagrams illustrating an example of the configuration of an aperture member. FIG. 10 is a diagram illustrating an example of a drawing operation. 1A and 1B are diagrams illustrating an example of a multi-beam irradiation area and a pixel to be written. 10 is a flowchart illustrating a drawing method according to the embodiment. 1A is a diagram showing the coverage rate of a first pixel, FIG. 1B is a diagram showing second pixels obtained by dividing the first pixel, and FIG. 1C is a diagram showing inside/outside determination information of the second pixel. FIG. 10 is a diagram showing the coverage of a second pixel. 1A is a diagram showing the position of the center of gravity of a pattern in a first pixel, and FIGS. 1B to 1D are diagrams for explaining a method for selecting a second pixel. 10A and 10B are diagrams illustrating the number of calculations of the coverage rate according to a comparative example.

Embodiments of the present invention will be described below with reference to the drawings. In the embodiments, a configuration using an electron beam will be described as an example of a charged particle beam. However, the charged particle beam is not limited to an electron beam, and an ion beam, etc. may also be used.

Figure 1 is a schematic diagram of a drawing device using a coverage calculation device according to an embodiment. As shown in Figure 1, the drawing device 100 includes a drawing unit 150 and a control unit 160. The drawing device 100 is an example of a multi-charged particle beam drawing device.

The drawing section 150 includes an electron lens barrel 102 and a drawing chamber 103. Inside the electron lens barrel 102, an electron gun 201, an illumination lens 202, an aperture member 203, a blanking plate 204, a reduction lens 205, a limiting aperture member 206, an objective lens 207, and a deflector 208 are arranged.

A continuously movable XY stage 105 is placed within the drawing chamber 103. A substrate 101, which is the target of drawing during drawing, is placed on the XY stage 105. The substrate 101 includes an exposure mask used when manufacturing a semiconductor device, or a semiconductor substrate (silicon wafer) on which a semiconductor device is manufactured. The substrate 101 also includes a mask blank coated with resist, on which nothing has yet been drawn. A mirror 210 for measuring the position of the XY stage 105 is also placed on the XY stage 105.

The control unit 160 has a control computer 110, memory 112, deflection control circuit 130, stage position detector 139, and storage devices 140 and 142 such as magnetic disk drives. These are connected to each other via a bus. Drawing data is input from the outside and stored in the storage device 140.

The control computer 110 has a rasterization unit 50, a dose map creation unit 52, an irradiation time calculation unit 54, and a drawing control unit 60. These functions may be configured as hardware such as electrical circuits, or as software. If configured as software, a program that realizes at least some of the functions may be stored on a recording medium and read and executed by a computer having a CPU. The recording medium that stores the program is not limited to removable media such as magnetic disks or optical disks, but may also be fixed recording media such as hard disk drives or memory. Information such as calculation results in the control computer 110 is stored in the memory 112 each time. The processing of the coverage calculation device according to this embodiment is performed by the rasterization unit 50 and the dose map creation unit 52.

Figure 2 is a conceptual diagram showing an example configuration of the aperture member 203. In Figure 2, a plurality of openings 22 are formed in the aperture member 203 in a matrix at a predetermined pitch. For example, 512 x 512 rows of openings 22 are formed in the vertical and horizontal directions (x and y directions). Each opening 22 is formed as a rectangle of the same dimensions. The openings 22 may also be circular.

Multi-beams 20a-e are formed when a portion of the electron beam 200 passes through each of these multiple openings 22. While an example is shown here in which two or more rows of openings 22 are arranged vertically and horizontally (x and y directions), this is not limiting. For example, there may be multiple rows in either the vertical or horizontal direction (x and y directions) and only one row in the other.

The blanking plate 204 has passage holes (openings) for the passage of each of the multi-beams at positions corresponding to the openings 22 of the aperture member 203 shown in Figure 2. A pair of electrodes for blanking deflection (blankers: blanking deflectors) is arranged across each passage hole. A deflection voltage based on a control signal from the deflection control circuit 130 is applied to one of the two electrodes, and the other is grounded.

Electron beams 20a-e passing through each passage hole are independently deflected by a blanker, and blanking control is performed. In this way, multiple blankers perform blanking deflection on the corresponding beams among the multi-beams that have passed through the multiple openings 22 in the aperture member 203.

Figure 3 is a conceptual diagram illustrating an example of a drawing operation. As shown in Figure 3, the drawing area 30 on the substrate 101 is virtually divided into a plurality of rectangular stripe areas 32 with a predetermined width in the y direction, for example.

First, the XY stage 105 is moved and adjusted so that the irradiation area 34 that can be irradiated with one irradiation of the multi-beam 20 is positioned at the left end of the first stripe area 32, or further to the left, and then drawing begins. When drawing the first stripe area 32, the XY stage 105 is moved, for example, in the -x direction, thereby relatively progressing drawing in the x direction. The XY stage 105 is moved, for example, continuously, at a predetermined speed.

After completing the drawing of the first stripe region 32, the stage position is moved in the -y direction, and the irradiation region 34 is adjusted so that it is positioned at the right end of the second stripe region 32, or further to the right, relative to the y direction. Then, by moving the XY stage 105, for example, in the x direction, drawing is performed in the same way in the -x direction.

The writing time can be reduced by alternating the direction of writing, such as writing in the x direction in the third stripe region 32 and writing in the -x direction in the fourth stripe region 32. However, this is not limited to alternating the direction of writing; writing in the same direction can also be performed when writing each stripe region 32. In one shot, multiple shot patterns, up to the same number as the number of openings 22, are formed at once by the multi-beams formed by passing through each opening 22 in the aperture member 203.

Figure 4 shows an example of a multi-beam irradiation area and a pixel to be drawn. In Figure 4, the stripe area 32 is divided into multiple mesh areas 40, for example, based on the beam size of the multi-beam. Each mesh area 40 becomes a drawing pixel area (drawing position). The example in Figure 4 shows a case where the drawing area of the substrate 101 is divided into multiple stripe areas 32, for example, in the y direction, with a width smaller than the size (shot size) of the irradiation area 34 that can be irradiated with a single irradiation of the multi-beams 20a-e. Note that the width of the stripe areas 32 is not limited to this and may be, for example, n times the size of the irradiation area 34 (n is an integer greater than or equal to 1).

The irradiation area 34 shows multiple pixels 24 (beam drawing positions) that can be irradiated with a single irradiation of the multi-beams 20a-e. In other words, the pitch between adjacent pixels 24 is the pitch between each beam of the multi-beam. In the example of Figure 4, one sub-pitch area 26 is formed by a square area surrounded by four adjacent pixels 24 and including one of the four pixels 24. Figure 4 shows a case where each sub-pitch area 26 is made up of 4 x 4 pixels.

In Figure 4, the size of the drawing pixel area is used as the beam size, but the smaller the size of the drawing pixel area, the more accurately the pattern shape is reflected, improving resolution and drawing accuracy.

Next, the operation of the drawing unit 150 will be described. The electron beam 200 emitted from the electron gun 201 (emitter) is illuminated almost perpendicularly by the illumination lens 202 onto the entire aperture member 203. As the electron beam 200 passes through each of the multiple openings 22 in the aperture member 203, multiple electron beams (multi-beams) 20a-e, each having a rectangular shape, are formed. The multi-beams 20a-e pass through corresponding blankers on the blanking plate 204. Each blanker individually deflects the passing electron beam 20 so that the beam is ON only for the calculated drawing time (irradiation time) and OFF at other times (performs blanking deflection).

After passing through the blanking plate 204, the multi-beams 20a-e are reduced by the reduction lens 205 and travel toward the central opening formed in the limiting aperture member 206. Electron beams deflected by the blanker of the blanking plate 204 to turn the beam OFF move away from the central opening of the limiting aperture member 206 (blanking aperture member) and are blocked by the limiting aperture member 206. On the other hand, electron beams not deflected by the blanker of the blanking plate 204 (deflected to turn the beam ON) pass through the central opening of the limiting aperture member 206.

The beams formed from when the beam is turned on until when it is turned off and that pass through the limiting aperture member 206 form one shot of beam. The multi-beams that pass through the limiting aperture member 206 are focused by the objective lens 207 to form a pattern image with the desired reduction ratio, and the deflector 208 deflects each beam (the entire multi-beam 20) in the same direction, irradiating each of the drawing positions (irradiation positions) on the substrate 101.

When the XY stage 105 moves continuously, the deflector 208 performs tracking control so that the beam drawing position (irradiation position) follows the movement of the XY stage 105. A laser is emitted from the stage position detector 139 toward the mirror 210 on the XY stage 105, and the position of the XY stage 105 is measured using the reflected light. Ideally, the multiple beams irradiated at one time will be aligned at a pitch obtained by multiplying the arrangement pitch of the multiple openings in the aperture member 203 by the desired reduction ratio described above.

During each tracking operation, the drawing device 100 shifts the drawing position in sequence and irradiates the multi-beams that become shot beams while following the movement of the XY stage 105.

Figure 5 is a flowchart illustrating a drawing method according to an embodiment.

The rasterization unit 50 reads the drawing data from the storage device 140 and calculates the pattern coverage within each first pixel region (hereinafter referred to as coverage) (step S1). The first pixel region is a virtual division of the drawing region (e.g., stripe region 32) into a mesh of a first size M1. The first size M1 is, for example, the size of one beam (individual beam) of a multi-beam. The coverage of the first pixel region is stored in memory 112.

Next, the rasterization unit 50 virtually divides each first pixel region into multiple second pixel regions in a mesh pattern with a second size M2 smaller than the first size M1. The second pixel regions correspond to the drawing pixel regions. Hereinafter, the first pixel region, second pixel region, and drawing pixel region will be referred to as the first pixel, second pixel, and drawing pixel, respectively. For each second pixel, the rasterization unit 50 checks whether the center of the second pixel is included in the pattern, and determines that a second pixel whose center is included in the pattern is a second pixel located inside the pattern (step S2). The center of a second pixel being included in the pattern means that the center of the second pixel is located on the pattern. A group of second pixels located inside the pattern approximates the pattern shape.

A second pixel whose center is not included in the pattern is determined to be a second pixel located outside the pattern. For each second pixel, inside/outside determination information determining whether it is located inside or outside the pattern is stored in memory 112.

For example, in step S1, the coverage rate for each first pixel is calculated as shown in FIG. 6(a). The coverage rate A for the first pixel is stored in memory 112 with, for example, 16-bit precision.

As shown in Figure 6(b), in step S2, a first pixel of a first size M1 is virtually divided into second pixels of a second size M2. In this example, the second size M2 is set to 1/4 the length of one side of the first size M1 (M1/M2 = 4), and the first pixel is virtually divided into 16 second pixels.

Then, it is checked whether the centers of the second pixels are included in the pattern. In the example shown in Figure 6(b), the centers of the four second pixels in the bottom row and the three second pixels first to third from the right in the second row from the bottom are included in the pattern, so these seven second pixels are determined to be located inside the pattern. The centers of the one second pixel in the second row from the bottom and first from the left, the four second pixels in the first row from the top, and the four second pixels in the second row from the top are not included in the pattern, so these nine second pixels are determined to be located outside the pattern.

For each second pixel, 1-bit inside/outside determination information, which is "1" if it is located inside the pattern and "0" if it is located outside the pattern, is stored in memory 112. For example, as shown in Figure 6(c), 16-bit inside/outside determination information is stored in memory 112 for 16 second pixels obtained by virtually dividing a first pixel.

Next, the dose map creation unit 52 virtually divides the drawing region (e.g., stripe region 32) into a plurality of proximity mesh regions (mesh regions for calculating proximity effect corrections) of a predetermined size in a mesh pattern. The size of the proximity mesh region is preferably set to approximately 1/10 of the range of influence of the proximity effect, for example, approximately 1 μm. The dose map creation unit 52 reads the drawing data from the storage device 140 and calculates, for each proximity mesh region, the coverage rate ρ of the pattern to be placed within that proximity mesh region.

Next, the dose map creation unit 52 calculates a proximity effect correction irradiation coefficient Dp(x) for correcting the proximity effect for each proximity mesh region. The proximity effect correction irradiation coefficient Dp(x) can be defined by a threshold model for proximity effect correction similar to conventional methods, using the backscattering coefficient η, the threshold dose threshold Dth of the threshold model, the coverage ρ, and the distribution function g(x).

Next, the dose map creation unit 52 calculates, for each drawing pixel (second pixel), the incident irradiation amount D (dose amount) to be applied to that drawing pixel. The incident irradiation amount D may be calculated, for example, as the value obtained by multiplying a preset base irradiation amount Dbase by a proximity effect correction irradiation coefficient Dp and the coverage rate ρ' of the drawing pixel.

The base dose Dbase can be defined, for example, as Dth/(1/2 + η).

In calculating the coverage ρ' of the drawing pixel, the dose map creation unit 52 reads out the coverage A and inside/outside determination information of the first pixel including the drawing pixel from the memory 112. The dose map creation unit 52 calculates the coverage ρ' of the drawing pixel whose inside/outside determination information is "1" from the following formula (1) using the read-out coverage A of the first pixel, the number N _IN of drawing pixels in the first pixel whose inside/outside determination information is "1", the size M1 of the first pixel, and the size M2 of the drawing pixel. In the following formula (1), (M1/M2) ² represents the number of drawing pixels in the first pixel.

ρ′=(A/N _IN )×(M1/M2) ² ...(1)

The dose map creation unit 52 sets the coverage ρ' of the drawing pixel (second pixel) whose inside/outside determination information is "0" to 0.

In the example shown in Figures 6(a) to (c), if the coverage rate A of the first pixel is set to 0.4, the coverage rate ρ' of the 16 drawing pixels within the first pixel will be as shown in Figure 7.

In this way, the dose map creation unit 52 calculates the incident dose D(x) for each drawing pixel, corrected for the proximity effect, based on the layout of multiple graphic patterns defined in the drawing data.

Then, the dose map creation unit 52 creates a dose map that defines the incident irradiation dose D for each drawing pixel in stripe units (step S3). The created dose map is stored, for example, in the storage device 142.

The irradiation time calculation unit 54 refers to the latest dose map and calculates the irradiation time t corresponding to the irradiation dose D for each drawing pixel (step S4). The irradiation time t is calculated by dividing the irradiation dose D by the current density. The irradiation time t for each drawing pixel is calculated as a value within the maximum irradiation time possible for one shot of the multi-beam 20. The irradiation time data is stored in the storage device 142.

In the drawing process (step S5), the drawing control unit 60 rearranges the irradiation time data in shot order according to the drawing sequence. The irradiation time data is then transferred to the deflection control circuit 130 in shot order. The deflection control circuit 130 outputs a blanking control signal to the blanking plate 204 in shot order, and outputs a deflection control signal to the deflector 208 in shot order. The drawing unit 150 draws a pattern on the substrate 101 using multiple beams with an irradiation amount calculated for each drawing pixel.

In the rasterization process, in the example shown in Figure 9(b), 32 bytes of memory were required to store the calculation results of the coverage rate for 16 pixels. However, in this embodiment, it is sufficient to store the coverage rate (16 bits) for the first pixel and the inside/outside determination information (16 bits) for 16 second pixels, reducing memory usage to 4 bytes. This also reduces the number of coverage rate calculations and the amount of calculation required.

In the above embodiment, the center of the second pixel obtained by virtually dividing the first pixel was checked to see if it was inside or outside the pattern, and the second pixel whose pixel center was inside the pattern was selected as the second pixel that approximates the pattern shape. However, the second pixel that approximates the pattern shape may also be selected taking into account the position of the center of gravity of the pattern at the first pixel.

For example, as shown in Figure 8(a), the rasterization unit 50 calculates the coverage rate A of the first pixel and determines the center of gravity CG of the pattern at the first pixel.

Next, as shown in Figure 8(b), the rasterization unit 50 selects the side closest to the center of gravity CG from the four sides H1 to H4 of the first pixel of the rectangle. In the example shown in Figure 8(b), the bottom side H1 in the figure is closest to the center of gravity CG.

Next, the rasterization unit 50 selects multiple second pixels (second pixel groups) that approximate the pattern shape within the first pixel. For example, it selects k columns of second pixel groups parallel to side H1, starting from side H1 closest to the center of gravity CG of the pattern toward side H3 opposite side H1. k is calculated using the coverage rate A of the first pixel, the size M1 of the first pixel, and the size M2 of the second pixel, using the following formula (2):

k=ceil(A×(M1/M2))...(2)

For example, if A = 0.4 and the first pixel is virtually divided into 16 second pixels (M1/M2 = 4), then k = 2, and as shown in Figure 8 (c), two rows of second pixels from side H1 toward side H3, i.e., the bottom two rows, are selected.

As shown in Figure 8(d), for each second pixel, one bit of selection information, which is "1" if selected and "0" if not selected, is stored in memory 112 along with the coverage rate A of the first pixel.

The dose map creation unit 52 calculates the coverage ρ' of the drawing pixels having selection information "1" from the following equation (3) using the coverage A of the first pixel, the number N _SEL of drawing pixels (second pixels) having selection information "1", the size M1 of the first pixel, and the size M2 of the drawing pixel.

ρ'=(A/N _SEL )×(M1/M2) ² ...(3)

The dose map creation unit 52 sets the coverage ρ' of the drawing pixel (second pixel) whose selection information is "0" to 0.

In this way, by selecting a group of second pixels that approximate the pattern shape based on the center of gravity of the pattern at the first pixel and assigning a coverage rate to these selected second pixels, the amount of calculation required for pixel coverage rates and memory usage can be reduced, just like in the above embodiment.

In the above embodiment, a multi-beam lithography system was described as an example of a charged particle beam system to which the coverage calculation system is applied, but the system can also be applied to a single-beam lithography system. Furthermore, the coverage calculation system can be applied not only to lithography systems but also to inspection systems. The inspection system compares the coverage of the second pixel calculated from the lithography data using the coverage calculation method according to the above embodiment with the coverage of the second pixel based on the measurement results of a pattern actually lithographed on a target substrate using this lithography data, and inspects whether they match.

The present invention is not limited to the above-described embodiments, and can be embodied by modifying the components within the scope of the spirit of the invention when implemented. Furthermore, various inventions can be created by appropriately combining multiple components disclosed in the above-described embodiments. For example, some components may be omitted from all of the components shown in the embodiments. Furthermore, components from different embodiments may be appropriately combined.

50 Rasterizing unit 52 Dose map creating unit 54 Irradiation time calculating unit 60 Drawing control unit 100 Drawing device 110 Control computer

Claims (7)

A method for calculating a pattern coverage rate for each pixel area obtained by dividing a pattern drawing area into a predetermined size by irradiating a charged particle beam, the method comprising:
virtually dividing the drawing area by a first size to generate a plurality of first pixel areas;
Calculating a pattern coverage of the first pixel region;
virtually dividing the first pixel region by a second size smaller than the first size to generate a plurality of second pixel regions corresponding to the pixel region;
selecting the second pixel area that approximates the pattern shape in the first pixel area;
A coverage calculation method for calculating the coverage of the selected second pixel region based on the pattern coverage of the first pixel region, the number of the second pixel regions in the first pixel region, and the number of the selected second pixel regions. The coverage calculation method according to claim 1, wherein, from among the plurality of second pixel regions, a second pixel region whose center is inside the pattern is selected as the second pixel region that approximates the pattern shape. Detecting a centroid of a pattern within the first pixel region;
selecting a first side closest to the center of gravity from among four sides of the rectangular first pixel region;
selecting k columns (k is an integer equal to or greater than 1) of second pixel regions parallel to the first side from the first side toward a second side opposite the first side as second pixel regions approximating the pattern shape;
The method of claim 1 , wherein k is a value based on the coverage of the first pixel region, the first size, and the second size. calculating an irradiation amount for each of the pixel regions using the coverage of the second pixel region calculated by the coverage calculation method according to any one of claims 1 to 3;
A charged particle beam writing method for writing a pattern on a substrate by controlling a charged particle beam based on the calculated dose. A coverage calculation device that calculates a pattern coverage for each pixel area obtained by dividing a pattern drawing area into a predetermined size by irradiating the area with a charged particle beam, the device comprising:
a rasterization unit that virtually divides the drawing area by a first size to generate a plurality of first pixel areas, calculates a pattern coverage rate of the first pixel areas, virtually divides the first pixel area by a second size smaller than the first size to generate a plurality of second pixel areas corresponding to the pixel areas, and selects the second pixels that approximate a pattern shape in the first pixel area;
A coverage calculation device that calculates the coverage of the selected second pixel region based on the pattern coverage of the first pixel region, the number of second pixel regions in the first pixel region, and the number of selected second pixel regions. The coverage calculation device according to claim 5, wherein the rasterization unit selects, from among the plurality of second pixel regions, a second pixel region whose center is inside the pattern as a second pixel region that approximates the pattern shape. a dose map creation unit that calculates an irradiation dose for each pixel region using the coverage of the second pixel region calculated by the coverage calculation device according to claim 5 , and creates a dose map that defines the irradiation dose for each pixel region;
an irradiation time calculation unit that calculates an irradiation time for each pixel region based on the dose map;
a writing control unit that controls an irradiation amount of the charged particle beam based on the calculated irradiation time;
A charged particle beam writing apparatus comprising: